Police refused to admit if they knew an undercover cop was part of a protest at Didcot Power Station or was the reason no one was ever arrested.

Former Metropolitan Police officer Mark Kennedy this week admitted being asked to assist with a publicity stunt to hang a banner off a tower in 2006.

But Thames Valley Police would not confirm whether they knew Mr Kennedy, 41, who infiltrated a group of environmental activists using the name Mark Stone, was one of the protesters.

Spokesman Rebecca Webber said: “For operational reasons, Thames Valley Police will neither confirm nor deny any intelligence regarding individuals or intelligence received surrounding this protest.”

No arrests were made at the protest five years ago.